Beam penetration color cathode ray tube



June 8, 1965 H. B. LAW ETAL BEAM PENETRATION COLOR CATHODE RAY TUBE 3 Sheets-Sheet 1 Filed Dec. 7, 1961 June 8, 1965 H. B. LAW ETAL BEAM PENETRATION COLOR CATHODE RAY TUBE 3 Sheets-Sheet 2 Filed D80. 7, 1961 m m w 5 m WW i Jim 8, 1965 H. B. LAW ETAL 3,188,507

BEAM PENETRATION COLOR CATHODE RAY TUBE Filed Dec. 7, 1961 5 Sheets-Sheet 3 mzhq 3,188,507 BEAM PENETRATION CGLGR CATHQDE RAY TUBE Harold B. Law, Princeton, Ni, John 3. Thomas, Levittown, Pa, and .iosef Gross, Princeton, Ni, assignors to Radio Corporation of America, a corporation of Delaware Filed Dec. '7, H61, Ser. No. 157,668 6 Claims. (Cl. 313-o9) This invention relates to cathode ray tubes of the type utilizing differential penetration of a luminescent screen by a plurality of different velocity electron beams to obtain plural color image re-creation, and particularly to the obtaining of coincidence of the plurality of rasters produced by the plurality of electron beams.

One type of cathode ray tube referred to above, which is particularly suited for home television use, includes a luminescent screen having three different phosphors which are disposed in superimposed layers, each of which is capable of emitting, for example, a different one of the three primary colors, red, green, and blue. The tube further includes three electron guns, each adapted to project a different velocity electron beam through a common deflection field and onto the luminescent screen. Electrons of the lowest velocity beam excite the first phosphor layer to produce light of a first color; electrons of the medium velocity beam penetrate the first layer and excite the second layer to produce light of a second color; and electrons of the highest velocity beam penetrate both the first and second layers and excite the third layer to produce light of a third color. Proper current intensity modulation of the three beams enables production of any desired mixture of these three colors.

In tubes of the type described above, unless preventive or corrective means are provided, the three raste-rs produced by the three electron beams are of different size. This is because the three beams, being of different velocity, are deflected different amounts by the common deflection field.

Substantially equal size and coincident red, green, and blue rasters can be obtained by diiierentially shielding the beams from portions of the common deflection field. Individual magnetic tubular shields are disposed around the two lower velocity beams and extend different distances into the common defl ction field. Thus, the two lower velocity beams, which in the absence of the magnetic tubular shields would be deflected the greater amounts by the common field, are subjected to difl erent selected fractions of the field and thereby eceive substantially the same amount of deflection as does the highest velocity, unshielded, beam.

In such tubes, magnetic tubular shields prevent creation of greatly different-size rasters and thus contribute greatly to raster coincidence, but the quality of register of the three rasters is still further improved by the present invention.

It is therefore an object of this invention to provide a new and improved plural beam cathode ray tube structure which contributes to the obtaining of high quality register of a plurality of rasters.

According to an embodiment of this invention, in a cathode ray tube of the type having magnetic beam shields, the magnetic tubular shield for the medium ve- Bdhhfid? Patented June 8, 1965 locity beam is made shorter and preferably larger in diameter than the magnetic tubular shield for the low velocity beam, and is axially positioned between the end planes of the low velocity beam shield. This serves to reduce the objectionable distortion caused by the presence of the magnetic tubular shields in the deflection field.

In the drawings:

FIG. 1 is a side elevation view partly in section and with parts broken away of a cathode ray tube incorporating the invention;

FIG. 2 is an end elevation view of the tube of FIG. 1;

FIGS. 3, 4-, and 5 are transverse sections of the oathode ray tube of FIG. 1 taken, respectively, along lines 33, 4-4, and 55;

FIG. 6 is a perspective of a portion of the cathode ray tube of FIG. 1;

FIGS. 7 and 8 are schematic illustrations of various magnetic beam shield embodiments used for the purpose of explaining the electron gun structure of FIG. 1;

FIG. 9 is a graph of a typical deflection field used in explaining FIGS. 7 and 8;

FIGS. 10 and 11 are schematic illustrations of the distortion effects of the shield embodiments of FIGS. 7 and 8, respectively, on a deflection field;

FIG. 12a is a schematic illustration of raster misregister caused by an improper electron gun orientation;

FIGS. 12b and 12c are schematic illustrations of the deflection fields which produce the raster misregister of FIG. 12a;

FIG. 13a illustrates raster register provided by the electron gun orientation of FIGS. 1-6;

FIGS. 13]) and are schematic illustrations of the deflection fields distortions provided by the electron gun orientation of FIGS. 1-6; and

FIGS. 14 and 15 are schematic illustrations of the effects of elements of the electron gun structure of BIG. 1 on the vertical deflection and horizontal deflection fields, respectively.

FIGS. 1, 2, 3, 4, 5, and 6 illustrate a cathode ray tube 8 comprising an evacuated envelope including a neck section 1%, a faceplate 12, and an interconnecting funnel section 14. Disposed Within the neck 10 is an electron gun assembly 15 comprising, for example, three electron guns 1o, 17, and 18 positioned side by side in a delta triangular arrangement symmetrically about the longitudinal axis of the gun assembly 15. In FIG. 1 gun .17 is hidden behind gun 16. The electron guns 16, 17, and 1e are respectively adapted to project lower, medium, and higher velocity electron beams through a common deflection zone 19 and toward the faceplate 12. For the purpose of brevity and clarity, the terms L beam, M beam, and H beam will be hereinafter used to refer respectively to the lowest velocity beam (and its gun to), the medium velocity beam (and its gun 1'7), and the highest velocity beam (and its gun 18).

A luminescent screen 20 on the faceplate 12 includes three layers 22, 24, and 26 of different phosphors, each of which luminesceses in a different one of the three primary colors, red, green, and blue. The tube 8 is operated so that electrons of the L beam will excite the first phosphor layer 26 to produce light of a first primary color; electrons of the iv beam will penetrate the first phosphor unease? layer 26 and excite the second phosphor layer 24 to produce light of a second primary color; and electrons of the H beam will penetrate both the first and second phosphor layers 26 and 24 and excite the third phosphor layer 22 to produce light of a third primary color. A metal backing layer 27 of, e.g., aluminum, is disposed on the phosphor layer 26 as is known in the art. If desired, the screen 20 may include nonluminescent separator layers between the phosphor layers to improve the operational characteristics of the screen.

'As an adjunct to the electron tube 8, a magnetic deflection yoke 28 is provided which closely encircles the envelope of the tube. The yoke 28, when suitably energized, is adapted to create two deflection fields capable of scanning the electron beams together over the luminescent screen 20 in mutually transverse, e.g., perpendicular, directions at different scan frequencies. In the preferred arrangement, horizontal and vertical magnetic deflection fields are established in the deflection zone 19 to cause the three separate beams of the electron guns 16, 17, and 18 to scan an orthogonal raster or pattern on the lumi nescent screen 20. I

As shown in FIG. 2, the faceplate 12 and luminescent screen 20 include a rectangular viewing area 29 and may themselves be circular or substantially rectangular which together with the viewing area preferably have a major axis XX and a minor axis YY perpendicular to each other. These axes are oriented for normal viewing with the axis XX horizontal and the axis YY vertical. In FIGS. 3, 4, and the axes XX and YY have been projected axially back along the tube 8 to the plane of these figures. The yoke 28 is so angularly oriented about the tube 8 and is of a type so adapted when excited with appropriate currents, that the electron beams scan on the screen 20 a rectangular raster having perpendicular major and minor axes which coincide with the axes XX and Each of the electron guns 16, 17, and 18 comprises a plurality of coaxial tubular electrodes. Each gun includes a tubular cathode 30 having an end wall which is coated with a suitable electron emissive material. Each cathode 30 is insulatingly mounted within a centrally apertured control grid cup 32. Disposed coaxially beyond the control grid cups 32, in the order named, are for each gun, a centrally apertured screen grid cup 34, a tubular focusing electrode 36, and a tubular anode 38. p

The anodes 38 are mounted on a cylindrical convergence cage 40 which is electrically common to all three of the electron guns 16, 17, and 18. The convergence cage 40 comprises a cup which has an end Wall 42 and which is closed at its open end with an end plate 43. Both the end wall 42 and the end plate 43 are provided with apertures 44, 45, and 46 which are coaxial respectively with the three electron guns 16, 17, and 18.

The cathodes 38, control grids 32, screen grids 34, and focusing electrodes 36 of the electron guns 16, 17, and 18 are individually connected to different ones of a plurality of lead-in conductors 50 which are sealed through the vacuum envelope in a stem base 52. Thus, each of these electrodes can be energized independently of the others to provide electron beams of different velocities which are independently focused in the region of the screen 20.

l n potential to the coating electrode 56, the anodes 38, and the luminescent screen 20.

The electrodes of each of the electron guns 16, 17, and 18 are maintained in fixed spaced coaxial relationship in a well-known manner such as by mounting them on three glass rods 59 which extend along the guns. Each of the electrodes 32, 34, 36, and 38 of each of the three guns is fixed to the glass rods in a manner similar to that illustrated for the focusing electrodes 36 in FIG. 3. As shown in FIG. 3, the electrode 36 of gun 18 is attached to a central arcuate section of a strap 60 Whose ends are embedded into two of the glass rods 59. The electrodes of guns 16 and 17 are mounted by similar straps 61 and 62 respectively to diflerent pairs of the glass rods 59. The strap 68 on the electrode 36 of the H gun 18 may be made of magnetic material for a purpose hereinafter described. Further details of the mounting of the electron guns 16, 17, and 18 have been omitted from the drawing for purposes of clarity.

Because the three electron guns 16, 17, and 18 are noncoaxial with respect to the tube 8, each gun being mounted slightly oif the longitudinal axis of the tube, both static and dynamic convergence of the three beams is provided to compensate for this oil axis mounting. Such convergence is in accordance with known color television receiver techniques.

Approximate convergence may be provided by mounting each gun at a small angle with respect to the longitu dinal axis of the tube 8 so that the three electron beams, when undeflected, are caused to converge approximately at a common point near the center of the luminescent screen 20. The angle which each gun makes with the tube axis is determined by the dimensions of the tube. In cathode ray tubes of the type described having a tube length of about 19 to 25 inches, this angle is in the order of 11.

Dynamic convergence may be provided as shown in FIG. 4. A separate pair of pole pieces 64 are disposed on opposite sides of each beam within the convergence cage 40. Associated with each pair of pole pieces 64 is a separate electromagnet 66 disposed externally of the tube envelope adjacent to the ends of the pole pieces. More refined'arrangements, such as those incorporating a pair of electromagnetic windings in place of the single winding 66, are known in the art but for the sake of brevity and clarity are not herein detailed. A Y-shaped magnetic shield 68 is disposed within the convergence Cage for shielding each beam from the convergence fields of the other beams.

Energization of the coils of the electromagnets 66 will impart to the respective electron beams a small radial directional component of deflection toward or away from the longitudinal axis of the tube 8. A varying current synchronized with, and related to, the amount of scanning deflection of the three beams is applied to each electromagnet 66 to provide the desired dynamic convergence of the three beams.

Also, in accordance with known techniques, all three beams are brought to a precise static convergence at the center of the luminescent screen 20 by means provided for adjusting the lateral position of one of the electron beams. This is accomplished by a magnetic field established in the path of the H beam by a permanent magnet assembly 69. In order to help shape the field of the magnet assembly 69 in the path of the H beam, the mounting strap 60 may in some instances be made of magnetic material. The field produced by the magnet assembly 69 is transverse to the direction of the magnetic field established between the pole pieces 64 for the H beam. This permits a lateral adjustment of the position of one of the three electron beams (viz, the beam produced by the electron gun 18 in the illustrated embodiment) in a direction which is normal to the radial adjustment of this same beam as provided by the convergence pole pieces 64.

If desired, the poles of the magnet assembly 69 may be dynamically energized to provide an additional means contributing to the shaping of the H beam raster for the propose of registering this raster with the rasters of the L and M beams.

The L beam gun 16 and M beam gun 17 are provided with-or have associated therewith-tubular magnetic shield members (i.e., magnetic shunts) 76 and 78, respectively, which are of different axial lengths and which extend coaxially with their respective guns. They may be mounted on the end plate 43. The tubular shields 7'6 and 78 extend from and are so positioned with respect to the electron gun apparatus that they are disposed within the deflection zone 19.

The M beam shield 78 is of shorter length and preferably of larger diameter than the L beam shield 76. The M beam shield is disposed alongside the L beam shield and is axially positioned between and spaced from the two planes perpendicular to the axis of the L beam shield at the ends therof. For the sake of brevity, this condition will hereinafter be described simply as the M beam shield being between the ends of the L beam shield. The L beam shield 76 is attached directly to the end plate 43. The M beam shield 78 is spaced from the end plate 43 by tandemly mounting it to the end of a first tubular nonmagnetic support member 80 which is in turn mounted to a smaller diameter tubular support 81 attached to the end plate 43. The nonmagnetic support 8t! may, for example, be attached to the end of the smaller support 31 by a plurality of interconnecting straps 82 (FIGS. 5 and 6). The purpose and advantage of the particular size relationship and relative dispositions of the L beam shield 76 and the M beam shield '78 will be hereinafter described in detail with reference to FIGS. 7, 8, 9, 10, and 11.

The electron gun apparatus is angularly oriented about the longitudinal axis of the tube 8 relative to the luminescent screen 2% and to the deflection yoke 28 so that the electron gun 18 producing the unshielded H beam is disposed in the central plane which is perpendicular to the scan produced by the higher frequency one of the two orthogonal deflection fields. According to present day practices in home television receivers the unshielded H beam would be disposed in the central vertical plane of the tube 8, i.e., the plane which contains the axis Y-Y of the screen and which is perpendicular to the axis XX. The orientation of the electron gun apparatus is such that the H beam gun 18 is preferably disposed above the other two guns 16 and 17 as is illustrated in FIGS. 1-6. The purpose and advantage of such an orientation of the electron gun apparatus are hereinafter described in detail with reference to FIGS. 12a, 12b, 120, 13a, 13b, and 13c.

Deflection field cnchancer elements 8 85 and S6, 87

of magnetic material are disposed on opposite sides of the H beam and M beam paths, respectively. The enhancer elements 84-87 are attached to the end plate 46 and extend, respectively, along the H and M beam paths into the deflection zone 19. The enchancer elements are preferably tubular members having a rectangular cross section as illustrated and are disposed with their sides parallel to the axes X-X and Y[, with one side of each pair of enhancers facing the other enhancer of the same pair. However, other cross sectional shapes, such as U-shaped rectangular channel members can be used. The purpose and advantages of the field enhancers 34-87 are hereinafter described in detail with reference to FIGS. 14 and 15.

By virtue of the different length of the shields 76 and 78 and their disposition in the deflection zone 19, the L beam and the M beam are shielded from the deflection field over different portions of their travel therethrough. The L and M beams are thus subjected to the deflection field for a shorter period of time than they would be in the absence of the shields 7t: and 78. By properly relating the lengths of the shields 7a: and 78 to the relative beam velocities and to the shape and length of the magnetic deflection field, the L and M beams are subjected to the deflection field for specific time durations which will result in their being deflected substantially the same amount as the tmshielded H beam. FIGS. 7-11 illustrate-the factors to be considered in selecting a proper relationship of shield dimensions and dispositions.

FIG. 7 illustrates part of an electron gun assembly similar to that of FIG. 1 except it has a shorter M beam shield '78 disposed alongside the L beam shield '76 at the distal end thereof. FIG. 8 illustrates part of an electron gun assembly similar to that of FIG. 1 except that it has a longer M beam shield 78" disposed alongside the L beam shield 76 at the proximal end thereof. FIG. 9 illustrates the variation with axial distance of the intensity of the transverse field such as provided by the yoke 28. The field, whose strength increases from some amount at the plane of the end plate 43 to a peak value and then decreases, is defined by a bell-shaped curve.

Since the deflection field increases in strength with increasing distance from the end plate 43, the percentage of the total field which a given length M beam shield will shield from the M beam increases as the shield is moved away from the end plate 43. Therefore, to provide a given amount of shielding, the M beam shield must be made shorter as it is moved away from the end plate 43. This is illustrated by the fact that the M beam shield '73 of FIG. 7 is shorter than the M beam shield 78 of PEG. 8.

If the M beam shield is spaced from the end plate 43, the M beam is deflected before reaching the M beam shield and will continue in a straight line along this deflected path as the beam passes through the M beam shield. If this shield is of insufiicient internal diameter, the beam will impinge upon the internal wall of the shield before it emerges therefrom. Thus, when the M beam shield is spaced from the end plate 43, it must be of sufficient diameter to prevent interference with the beam. Accordingly, the M beam shield 78 is made larger in diameter than the L beam shield 76 in the electron gun apparatus 15 of FIG. 1.

FIG. 10 illustrates the distorted shape of the defiection field lines lit? in planes which intersect both the L beam shield and the M beam shield, such as plane B-B of FIG. 7 and plane C--C of FIG. 8. This type of distortion tends to produce an H beam raster 91 whose right side vertical dimension is greater than its left side. FIG. 11 illustrates the distorted shape of the deflection field lines 92 in planes which intersect only the L beam shield such as plane A-A of FIG. 7 and plane DD of FIG. 8. This type of distortion tends to produce an H beam raster 93 whose left side vertical dimension is greater than its right side. FIGS. 10 and 11, it should be noted that these il1us trations depict only the shape of the field and not the strength of the field. Field strength is illustrated by FIG. 9.

Where a magnetic shield is positioned in a magnetic field, the flux lines are distorted toward, and concentrated adjacent to, the shield so as to follow the path of least reluctance. in the case of the field distortion in a plane cutting both shields (PEG. 10), the greater distortion, or flux concentration, is produced by the M beam shield because of its larger diameter. in the case of the field distortion in a plane cutting only the L beam shield (FIG. 11), the distortion, or fiux concentration, is produced only by the L beam shield because of the absence of the M beam shield. Thus, in one case (FIG. 10) more flux lines are distorted or bent to the left in the region of the incipient l-I beam raster and in the other case (PEG. 11) to the right. Since the lower boundary of the incipient H beam raster tends to be contoured perpendicularly to the flux lines, the vertical dimension of the raster is greater on its right side in one case (PEG. ill) and on its left in the other case (FIG. 11).

In referring to the field distortions of tially parallel.

That is, the distortions of FIGS. 10 and 11 produce opposite effects on the incipient H beam raster.

Although the field distortion as illustrated by FIG. 10 is the same shape at the plane B-B as it is at the plane CC, the distortion has a greater effect at the plane B B because the field intensity at that plane is much greater. Therefore, the net resultantdistortion of the H beam raster can be symmetrized, or made less objectionable, by axially moving the M beam shield until the FIG. 10 type distortion is of a strength which balances the FIG. 11 type distortion. This is achieved by axially positioning the M beam shield between the ends of the L beam shield as illustrated in FIGS. 1 and 6. For a given field strength and shape (which depends upon the yoke used) and for every ratio of diameters of the two shields there is one axial position or" the shorter M beam shield between the end planes of the longer L beam shield which provides the least asymmetry of the raster scanned by the unshielded H beam. As an example of one actual embodiment of this teaching, wherein the tube 8 of FIG. 1 is operated with a standard deflection yoke 28 and with the L beam at 10 kv. velocity, the M beam at 16 kv., and the H beam at 22 kv.; the L beam shield 76 is A inch in diameter and 1% inches long, the M beam shield 78 is inch in diameter and /8 inch long, and the M beam shield is axially positioned inch back from the distal end of the L beam shield (the L beam shield 76 extends inch closer to the luminescent screen than does the M beam shield '78).

In establishing the optimum relationship of diameters, lengths, and axial positions of the two shields, the M beam shield is disposed between the ends of the L beam shield and various parameters are then adjusted to obtain the least asymmetry of the H beam raster. The length of the M beam shield is selected to produce the proper overall size M beam raster; the diameter of the M beam shield is then selected so as to just avoid the M beam from striking the shield when fully deflected; and the axial position of the M beam shield is then selected to obtain the least asymmetry of the H beam raster. A change of any one of these parameters may call for a slight re-adjustment of the others in order to obtain the optimum relationships producing minimum asymmetry of the H beam raster.

FIG. 12a is representative of the type of raster distortion and misregister that is caused by an electron gun orientation other than that of the unshielded H beam gun in the central vertical plane of the tube. In FIG. 12a an H beam raster 109, an M beam raster 191 and an L beam raster 102 are illustrated. The misregistry or" the rasters 100, 101, and 102 is characterized by a crossover 103 of the lower boundaries of the H beam raster 1% and the M beam raster 161. Such a crossover is due to extreme asymmetry of distortions caused by the L beam and M beam shields when the electron gun orientation is other than that taught with reference to FIGS. 1-6.

FIGS. 12b and 12c illustrate the asymmetry of the deflection field distortion in a plane cutting both shields produced by the L beam shield '76 and the M beam shield 78 when the gun orientation is with the L beam gun 16 in the central vertical plane of the tube. Such an orientation results in the crossover misregistry of FIG. 12a. FIG. 121) shows the distortion of flux lines 108 of the horizontal deflection field, and FIG. 120 shows the distortion of the flux lines 11% of the vertical deflection field.

FIG. 13a illustrates the improved results obtained by the electron gun orientation as taught with reference to FIGS. 16. In FIG. 13a an H beam raster 112, an

,M beam raster 114, and an L beam raster 115 are illustrated. These rasters are characterized by a nesting thereof wherein they are either registered with each other or the corresponding boundaries of the rasters are substan- In FIG. 13a the spacing between rasters 5 is exaggerated for the purpose of more clearly illustrating the nesting relationship. The rasters have substantially the same shape and difler slightly from each other only in their overall size. i

FIGS. 13b and 130 illustrate the symmetrized'distortion in a plane cutting both shields of the horizontal and vertical deflection fields, respectively, which is obtained by orienting the H beam gun 18 in the vertical central plane of the tube. In FIG. 13b the flux lines of the horizontal deflection field are indicated at 118; in FIG. 13c the flux lines of the vertical deflection field are indicated at 120.

By comparing FIG. 12b with 13b, and 120 with 13c, the improved symmetry about the vertical central plane of the tube which results from positioning the H beam gun in that plane is. apparent. Whereas only one undesirahle electron gun orientation is herein illustrated (FIGS. 12a, 12b, and 12c), other orientations (other than the H beam in the vertical'central plane of the tube) produce distortions similar to those illustrated in FIGS. 12b

and 12c.

FIGS. 14 and 15 illustrate the effect of magnetic en hancers such as the enhancers ed and on the vertical deflection and horizontal deflection fields, respectively, of the H beam. If a pair of enhancers are disposed in both the horizontal and vertical fields, they will enhance the strength of the deflection field in one direction, e.g., horizontal, and decrease the'strength of the field in the perpendicular direction, e.g., vertical, in the space be tween the enhancers which is the region of the electron beam path with which they are associated. If the horizontal and vertical deflection fields are not coextensive and the enhancers are disposed inonly one of the fields, they will affect only that field. Since enhancers are placed adjacent a particular beam path and primarily associated therewith (e.g., enhancers $54 and 85 for the H beam), they primarily affect the deflection field only locally for the particular beam associated therewith. Enhancers act as magnetic conductors which are placed in the gap between a pair of deflection coils and thus decrease the reluctance of the deflection field flux path in the localized area occupied by the enhancers.

The'pair of H beam enhancers 84 and 85, being aligned in a horizontal plane,'c onduct the horizontally directed flux lines producing the vertical H beam'deflection and thus enhance the vertical deflection of the H beam and thereby expand the H beam raster vertically.

In FIG. 14 the effect of the enhancers 84 and 85 are shown on the flux lines 122 of the vertical deflection field of the H beam. In following the path of least reluctance, the flux lines 122 are bent toward and pass through the enhancers 84 and 85. The enhancers maybe thought of as gatheringthe flux lines from surrounding areas and concentrating them. Since the enhancers are arranged serially in the direction of the flux lines, the flux in the area between the enhancers 84 and 85 is concentrated and provides a stronger vertical deflection field of the H beam than would otherwise exist without the enhancers. This serves to expand the height of the H beam raster. At the same time, as shown in FIG. 15, the flux lines 124 of the horizontal H beam deflection fieldare bent toward and pass through the enhancers 84 and 85. Since the enhancers are arranged in parallel in the direction of the horizontal deflection flux lines, they gather flux which would otherwise pass between the enhancers, and thereby the enhancers lower the flux concentration in that area and provide a weaker'horizontal deflection field for the H beam; This results in a horizontal contraction of the H' beam raster. The vertical expansion and horizontal contraction of the resulting H beam raster are additive in effecting a change of the aspect ratio of the raster.

In the delta arranged 3-gun assembly of FIGS. 16, enhancers are provided to not only vertically expand the H beam raster but to also horizontally expand the M are beam raster. This can be done with a separate pair of enhancer members for each of the two beams, one pair horizontally aligned and the other pair vertically aligned. However, in the specific embodiment shown, the H and M beams are so closely spaced that room is not available for separate pairs of enhancers for each of the beams without an enhancer of one pair interfering with an en hancer of the other pair. This problem is overcome by making the enhancer 85 common to both a first pair of enhancers (84 and S) for the H beam and a second pair of enhancers (85 and $7) for the M beam. For this purpose both the horizontal and vertical cross-sectional dimensions of the enhancer 85 is made of sufficient magnitude to provide the desired field enhancements.

Although enhancer 35' pairs with enhancer 87 to provide the primary horizontal deflection field enhancement for the M beam, available space in the neck A of the tube 3 does not permit the enhancer 85 to be centered over the M earn. Therefore, a fourth enhancer 86 is provided between the enhancer 85 and the M beam (centrally thereover) to shape the horizontal deflection field in the region of the M beam by more nearly vertically orienting the fiux lines thereof. The enhancers 85 and 86 can be provided as a single integral member, as two separate members attached to each other, or as two separate slightly spaced members as shown. The enhancers 85, 36, and 87 function with respect to the M beam in a manner somewhat similar to the manner described with reference to FIGS. 14 and in which the enhancers 84 and 85 function with respect to the H beam.

By virtue of their ability to selectively affect only one raster and, moreover, to selectively expand and contract the selected raster so as to change its aspect ratio, these enhancers provide a means for raster shaping.

The relative percentage of expansion and contraction of a raster to afiect its aspect ratio is dependent upon the horizontal and vertical cross-sectional dimensions of the enhancers and the spacing between them. An increase of the horizontal cross-sectional dimension of the enhancers 8d and 85 further enhances the field illustrated in FIG. 14 and causes greater expansion of the H beam raster in vertical direction. An increase of the vertical cross-sectional dimension of the enhancers 84 further reduces the intensity of the field illustrated in FIG. 15 and causes greater contraction of the H beam raster in the horizontal direction. -enerally speaking, the closer together a pair of enhancers are positioned, the greater their effect. If the enhancers 84- and 85 are positioned closer together, the bowing out of the flux lines of the vertical H beam deflection field (FIG. 14) between the enhancers will be decreased and the field thus strengthened. The resulting H beam raster will be further expanded vertically. At the same time the horizontal H beam deflection field (FIG. 15) between the enhancers will be weakened and the resulting H beam raster further contracted horizontally.

The raster size is a function of the length of the enhancers along the beam path. An increase of the length of the enhancers serves to increase the raster size without materially changing the aspect ratio.

it may be desired to provide an electron beam with both a shield tube and enhancers, such as the M beam of tube 8 which has both the shield tube 78 and the enhancers 85, 86, and 37. In such case the shield tube is axially staggered with, and adequately spaced from, the enhancers as is shown in FIG. 6. This permits both the shield tube and the enhancers to separately exert their own actions on a different portion of the deflection field without interference by the other. If the shield tube 78 were positioned too close to, or in contact with, the enhancers 85, $6, and 87, the flux lines between the enhancers would be shunted through the shield, thus reducing the effect of the enhancers.

The nnomagnetic support 81 may be such as to permit the enhancers 36 and 37 to be disposed closer together and thus closer to the beam path. For example, if tubular, the support 31 may be of smaller diameter than the shield tube 78. Alternatively, the support 81, as well as the support 80, could, for example, consist of one or more nonmagnetic support wires, straps, or the like. Support 81 may even be omitted altogether and the nonmagnetic support mounted directly on the ends of the enhancers 86 and 87.

The invention has been described in terms of specific examples and embodiments. However, various changes and modifications may be made therein without departing from the spirit and scope of the invention as defined by the following claims.

What is claimed is:

l. A cathode ray tube comprising a luminescent screen and three electron guns for projecting three different velocity electron beams through a common deflection zone toward said screen, two of said guns having mag netic beam shields positioned in said deflection zone, one of said shields being shorter than the other and axially disposed between and spaced from the ends of said other shield.

12. A cathode ray tube comprising a luminescent screen and three electron guns disposed side-by-side in triangular array for projecting three different velocity electron beams through a common deflection zone toward said screen, two of said guns having magnetic tubular beam shields positioned in said deflection zone, one of said shields being shorter and of greater diameter than the other and axially disposed between the ends of said other shield.

3. A cathode ray tube comprising a viewing screen; an electron gun assembly of three electron guns disposed side-by-side in triangular array for projecting three different velocity electron beams through a common deflection zone toward said screen; and two magnetic tubular beam shields of unequal length surrounding the beam paths of two of said guns, extending from said assembly, and positioned in said deflection zone; the shorter of said shields being axially disposed between the ends of the longer shield and closer to the distal end of said longer shield than to the proximal end thereof.

4. A cathode ray tube comprising a viewing screen and an assembly of three electron guns disposed side-by-side in triangular array for projecting three different velocity electron beams through a common deflection zone toward said screen, said assembly including a convergence cage at the end thereof nearest said screen, two magnetic tubular beam shields of unequal length surrounding the beam paths of two of said guns and supported from said cage and positioned in said deflection zone, the longer of said tubular shields substantially abutting said cage, the shorter of said shields being axially spaced from said cage, the distal end of said longer shield being disposed farther from said cage than is the distal end of said shorter shield.

5. A cathode ray tube comprising a luminescent viewing screen and an electron gun assembly including three electron guns disposed side-by-side in delta array and for projectin three different velocity electron beams toward said screen through a common deflection zone for establishing a common deflection field therein, a first magnetic tubular shield surrounding the path of a first one of said beams in said deflection zone, and a second magnetic tubular shield surrounding the path of a second one of said beams in said deflection zone, one of said shields being shorter and of larger diameter than the other and axially disposed between and spaced from the ends of said other shield, the relative lengths, relative diameters, and relative axial dispositions of said shields being such that for given beam velocities and a given field shape and strength, substantially equal size rasters are scanned by the three beams and the deflection field distortions caused by the two shields have substantially corresponding effects on the raster of the third beam which is scanned through the two field distortions.

6. A cathode ray tube comprising a luminescent screen, three electron guns disposed side-by-side in delta array for projecting three different velocity electron beams through a common deflection zone and toward said screen, a first magnetic tubular shield substantially /8 inch long and substantially inch in diameter surrounding the path of one of said beams in said deflection zone, and a second magnetic tubular shield substantially 1% inches long and substantially 4 inch in diameter surrounding and the path of another of said beams in said deflection zone and extending axially substantially inch closer to said screen than does said first shield.

References Cited by the Examiner UNITED STATES PATENTS 2,943,232 6/60 Roberts 3l3--70X GEORGE N. WESTEY, Primary Examiner. 

5. A CATHODE RAY TUBE COMPRISING A LUMINESCENT VIEWING SCREEN AND AN ELECTRON GUN ASSEMBLY INCLUDING THREE ELECTRON GUNS DISPOSED SIDE-BY-SIDE IN DELTA ARRAY AND FOR PRJECTING THREE DIFFERENT VELOCITY ELECTRON BEAMS TOWARD SAID SCREEN THROUGH A COMMON DEFLECTION ZONE FOR ESTABLISHING A COMMON DEFLECTION FIELD THEREIN, A FIRST MAGNETIC TUBULAR SHEILD SURROUNDING THE PATH OF A FIRST ONE OF SAID BEAMS IN SAID DEFLECTION FIELD THEREIN, A FIRST MAGNETIC TUBULAR SHIELD SURROUNDING THE PATH OF A FIRST ONE OF SAID SAID BEAMS IN SAID DEFLECTION ZONE, ONE OF SAID SHIELDS BEING SHORTER AND OF LARGER DIAMETER THAN THE OTHER AND AXIALLY DISPOSED BETWEEN AND SPACED FROM THE ENDS OF SAID OTHER SHIELD, THE RELATIVE LENGTHS, RELATIVE DIAMETERS, AND RELATIVE AXIAL DISPOSITIONS OF SAID SHIELDS BEING SUCH THAT FOR GIVEN BEAM VELOCITIES AND A GIVEN FIELD SHAPE AND STRENGTH, SUBSTANTIALLY EQUAL SIZE RASTERS ARE SCANNED BY THE THREE BEAMS AND THE DEFLECTION FIELD DISTORTIONS CAUSED BY THE TWO SHIELDS HAVE SUBSTANTIALLY CORRESPONDING EFFECTS ON THE RASTER OF THE THIRD BEAM WHICH IS SCANNED THROUGH THE TWO FIELD DISTORTIONS. 